Method of manufacturing acrylonitrile polymers having an excellent whiteness

ABSTRACT

AN ACRYLONITRILE POLYMER USEFUL FOR PRODUCING ACRYLONITRILE SYNTHETIC FIBER HAVING AN EXCELLENT WHITENESS AND A SUPERIOR HEAT STABILITY IS PREPARED BY THE POLYMERIZATION METHOD WHEREIN THE ACRYLONITRILE IS POLYMERIZED OR COPOLYMERIZED IN THE PRESENCE OF A REDOX CATALYST AT A CONCENTRATION OF MONOMER TO BE POLYMERIZED IN WATER WHICH CONCENTRATION IS SO ADJUSTED THAT THE CONCENTRATION OF NONPOLYMERIZED MONOMER REMAINING IN WATER WHICH RELATES TO THE YIELD OF THE RESULTANT POLYMER IS ON OR WITHIN THE QUADRILATERAL ABCD DEFINED IN THE ACCOMPANYING DRAWING.

May 28, 1974 YASUSHl JOH ETAL 3,813,372

METHOD OF MANUFACTURING ACRYLONITRILE POLYMERS HAVING AN EXCELLENTWHITENESS Original Filed July 15. l97l kbz fig 5(70555) mews) 65 70 so90 I00 YIELD OF POLYMER /0) United States Patent 3,813,372 METHOD OFMANUFACTURING ACRY- LONITRILE POLYMERS HAVING AN EXCELLENT WHITENESSYasushi Job and Teruhiko Sugimori, Otake, Japan, as-

;ignors to Mitsubishi Rayon Company Limited, Tokyo,

apan

Continuation of abandoned application Ser. No. 162,921,

July 15, 1971. This application Feb. 23, 1973, Ser. No. 335,121

Claims priority, application Japan, July 27, 1970, 45/64 979 Int. Cl.C08f 3/76, 15/02, 15/22 US. Cl. 260-88.7 R 1 Claim ABSTRACT OF THEDISCLOSURE CROSS REFERENCE TO RELATED APPLICATIONS This application is acontinuation of our co-pending application, Ser. No. 162,921, filed July15, 1971 and now abandoned.

The present invention relates to a method of manufacturing acrylonitrilesynthetic polymers having an excellent whiteness, more particularly,relates to a method of manufacturing acrylonitrile synthetic polymersusable for forming acrylonitrile synthetic fibers having an excellentwhiteness by polymerizing acrylonitrile alone or copolymerizing at least50% by weight of acrylonitrile and the balance of a monomer capable ofcopolymerizing with the acrylonitrile in the presence of a redoxcatalyst containing nitrous acid or its salt and a reducing sulfoxylcompound.

It is well-known that there are various catalysts for manufacturing theacrylonitrile synthetic polymers. The catalysts include substances whichthemselves have the ability of initiating the polymerization andcompositions consisting of two or more substances having catalyticproperty for the polymerization. Particularly, it is known that theso-called redox catalysts are effective for the production of theacrylonitrile synthetic polymers. The redox catalyst consists of amixture of an oxidizing agent and a reducing agent each itself having nocatalytic property for the polymerization. Generally, the utility of thepolymerization catalyst must be estimated not only on the basis of itsinitiating and accelerating properties for the polymerization but on thebasis of properties of the product obtained by utilizing the catalyst.In view of the above estimation, it is relatively diflicult to find acatalyst which is elfective for producing the polymer having superiorproperties at a high efiiciency.

As is widely known, the fiber-forming acrylonitrile polymers arerequired to have various properties necessary for manufacturing thesynthetic fiber, and the qualities of the acrylonitrile synthetic fiberdepend on the qualities of the acrylonitrile polymer to be convertedinto the fiber. This dependance is similar to that of the othersynthetic fibers, for example, polyamide, such as nylon 66, andpolyester fibers.

Patented May 28, 1974 The fiber-forming acrylonitrile polymers arerequired to have various excellent properties such as processabilitiesin the fibers manufacturing process.

The required processabilities include (1) a superior transportationproperty of the polymer which relates to formal properties of thepolymer, (2) a high stability in a process for feeding the polymer intoa polymer solution-preparing system which stability depends on bulkinessof the polymer powder and size and shape of the polymer particle andmeans a property such that the polymer can be fed into the polymersolution-preparing system at a uniform feeding rate with no formation ofthe so-called bridge with the polymer powder, (3) a high stability inspinning process and (4) a high processability in drawing process ordraft-cutting process, for example, tarbo stapler. The fiber-formingacrylonitrile polymers have a further requirement that the acrylonitrilesynthetic fibers produced from the polymer can be spun into a yarnhaving excellent quality in a favorable spinning condition, and have ahigh whiteness, a superior heat stability, a good dyeing property andnon-variation in dyeing exhaustion level, and the article prepared fromthe acrylonitrile synthetic fibers has a good hand feeling.

In order to prepare the desirable polymer sufficiently satisfying theabove-mentioned various requirements, it is important that the catalystis carefully selected, the polymerization is carried out under pertinentconditions, and the quality of the product is suitably controlled.

In the case Where the above-mentioned requirements are not satisfied, itis impossible to obtain the high quality acrylonitrile polymer howeverthe conditions for processing the spinning and other steps thereafterare 'varied.

From the above-viewpoint, the inventors have carefully studied theproduction process of the fiber-forming acrylonitrile polymer,particularly, the polymerization catalyst and the polymerizationcondition, more particularly, the redox polymerization catalystcontaining nitrous acid or its salt and a reducing sulfoxyl compound.From the study, the inventors have found a polymerization conditioneffective for obtaining an acrylonitrile polymer or copolymer havingexcellent properties such as an excellent whiteness and a superiorheat-stability and hence the present invention.

An object of the present invention is to provide a method ofmanufacturing an acrylonitrile polymer which has an excellent whitenessand is useful for producing an acrylonitrile synthetic fiber having anexcellent whiteness and a good heat stability.

Such object can be accomplished by the method of the present inventionwherein acrylonitrile monomer alone or a mixture of the acrylonitrilemonomer and another monomer capable of copolymerizing with theacrylonitrile is polymerized in water in the presence of a redoxcatalyst containing nitrous acid or its salt and a reducing sulfoxylcompound at a concentration of the monomer or monomers in water soadjusted that when the polymerization is completed at an expected yieldof the resultant polymer, a concentration of non-polymerized monomerremaining in Water is in a range specified hereinafter.

The concentration (C) of the non-polymerized monomer in water iscalculated according to the equation:

C (percent) The drawing is a graph for defining the range ofconcentration in percent of non-polymerized monomer remaining in watercorresponding to an expected yield in percent of the resultant polymer,in which range the polymerization according to the method oi the presentinvention is carried out eifectively.

From a systematic study by the inventors, it was found that when theconcentration of monomer to be polymerized in water is adjusted so thatthe concentration. of nonpolymerized monomer remaining in water which iscalculated on the basis of the expected yield of the polymer to beproduced is on or within the quadrilateral ABCD defined in theaccompanying drawing, the resultant polymer has an excellent whitenessand a superior heat stability and is very useful for producing theacrylonitrile synthetic fiber.

In the accompanying drawing, the ordinate represents the concentrationof non-polymerized monomer in water in percentage by weight and theabscissa represents the yield of the polymer in percentage by weight andthe quadrilateral ABCD is defined by co-ordinates A (70, B (70, 3.33), C(96, 0.44) and D (96, 1.33).

Therefore, it is obvious that the method of the present invention can beapplied only to the polymerization which is carried out under anexpected yield of the polymer of from 70 to 96% by weight.

The catalyst usable for the polymerization according to the method ofthe present invention consists of a mixture of nitrous acid or its salt,for example, sodium nitrite, potassium nitrite, ammonium nitrite,calcium nitrite and magnesium nitrite, and a reducing sulfoxyl compoundfor example, sulfurous acid, sulfites such as sodium, potassium andammonium sulfites, bisulfites such as sodium, potassium and ammoniumbisulfites, and metabisulfites such as sodium and potassiummetabisulfites. Catalysts other than the above-mentioned redox catalystcan not be applied to the polymerization according to the method of thepresent invention. Accordingly, it should be noted that the method ofthe present invention is etfective only for polymerization utilizing theabove-specified redox catalyst and resulting in the yield of polymer aslimited above.

The reason why the method of the present invention is ,etfective onlyfor the above restricted polymerization is not clear as yet. However, itis supposed that the redox catalyst is closely related with theradical-forming behavior of the monomer and the features of theresultant polymer slurry.

In the performance of the method of the present invention, each of thecatalyst components may be added separately to the polymerization systemor may be added into the system after the components have beenpreviously mixed and reacted with each other.

The method of the present invention can be applied to the polymerizationof acrylonitrile alone or to the copolymerization of at least 50% byweight of acrylonitrile with the balance of monomer capable ofcopolymerizing with the acrylonitrile.

The monomer capable of polymerizing with the acrylonitrile may beselected from ethylenically unsaturated monomer such as vinyl acetate,ethyl acrylate, methyl acrylate, methyl methacrylate, methacrylonitrile,methylene glutaronitrile, vinyl bromide, vinyl chloride, yiuylidenechloride, acrylamide, N,N'-substituted acrylamides, methacrylamide,acrylic acid and methacrylic acid. The group of monomer includes, of asa matter of course, basic or strongly acid monomers useful for modifyingthe dyeing property of acrylonitrile polymer, for example, vinylpyridines, dimethyl amino ethyl acrylate and methacrylic sulfonic acid.

It is preferable that the polymerization according to the method of thepresent invention is carried out at a tempearture of 40 to 60 C.Further, it is preferable that the polymerization according to themethod of the present invention is performed at a pH of 2.0 to 3.0.

The feature of the method of the present invention is explained in moredetail by the following examples which include comparison examples forclearly illustrating the effect of the method of the present invention.

In the examples, the whiteness of the fibers is indicated by a ratio ofreflectivity of the fiber with respect to that of a magnesium oxideplate which reflectivity is determined by means of an automaticrecording spectrophotometer (type EPU-2) made by Hitachi Seisakusho,Japan.

EXAMPLE 1 In order to prepare acrylonitrile polymer from acrylonitrilein a polymerization yield of 72% based on the initial weight of theacrylonitrile, 100 parts by weight of acrylonitrile were mixed with 600parts by weight of water, 7.2 parts by weight of sodium hydrogensulfiteand 0.8 parts of sodium nitrite. In this case, it was expected that,after completing the polymerization, the concentration of thenon-polymerized acrylonitrile which remained in water would be 4.67% byweight. A point having the co-ordinate (72, 4.67) is contained withinthe quadrilateral ABCD defined in the accompanying drawing.

The mixture was adjusted to a pH of 2.6 by using sulfuric acid andsubjected to polymerization at a temperature of 45 C. for 5 hours. Theresultant polymer was filtered, washed with water and dried. The yieldof the resultant polyacrylonitrile was 72% by weight which was the sameas that expected previously. Therefore, the non-polymerizedacrylonitrile remained in the mixture in a concentration of 4.67% whichwas equal to that expected previously.

The polyacrylonitrile was dissolved in dimethyl formamide in aconcentration of 28% by weight in order to prepare a spinning solution.The spinning solution was subjected to the conventional dry-spinningprocess to prepare acrylonitrile synthetic filaments. The resultantfilaments were drawn, washed with water, treated with an oil agent andthen dried under conventional conditions. The dried filaments werefurther heat-treated at a temperature of 135 C. in order to redox them.The acrylonitrile synthetic fiber thus heat-treated had a whiteness of98.6. This result shows the fact that the polyacrylonitrile which wasprepared by the process according to the present invention, is highlyuseful for producing the acrylonitrile synthetic fiber having anexcellent whiteness and a superior heat stability.

For comparison, parts by weight of acrylonitrile were mixed with 1200parts by weight of water, 4.5 parts by weight of sodium hydrogensulfiteand 0.26 parts by weight of sodium nitrite. The mixture was subjected topolymerization at a temperature of 52 C. for 10 hours. 67 parts byweight of polymer was obtained. This corresponds to a yield of about 84%based on the initial weight of the acrylonitrile.

The concentration of the non-polymerized acrylonitrile which remained inthe water was 1.07% by weight. It is clear that the point having theco-ordinates (84, 1.07) lies outside the quadrilateral ABCD of theaccompanying drawing.

A spinning solution containing 29% by weight of the resultant polymer indimethyl formamide was dry-spun, and the resultant filaments were drawn,washed with water, dried and then heated-relaxed at a temperature of 135C. The resultant filaments thus heat-relaxed had a whiteness of 92.0which is lower than that of the example.

For further comparison, parts by weight of acrylonitrile were mixed with250 parts by weight of water, 4.0 parts by weight of sodiumhydrogensulfite and 0.20 parts by weight of sodium nitrite. The mixturewas ad justed to a pH of 2.7 by using sulfuric acid and subjected topolymerization at a temperature of 45 C. for 6 hours. The resultantpolymer was filtered, washed with water and then dried. 75 parts byweight of the polymer was obtained in a yield of 75% based on theinitial weight of acrylonitrile. The concentration of non-polymerizedacrylonitrile in water was 10%. The point having coordinate (75, 10)lies outside the quadrilateral ABCD. The resultant copolymer containedsome solid masses of the polymer. The polymer was dissolved in dimethylformamide in a concentration of 29% by weight. The resultantacrylonitrile polymer was converted into filaments by conventional dryspinning and drawn in hot water at a draw ratio of 3.5 and thenheat-relaxed at a temperature of 145 C.

The resultant acrylonitrile synthetic filament had a low whiteness of92.0.

EXAMPLE 2 In order to prepare an acrylonitrile copolymer in a yield of73% based on the initial weight of the comonomers, 94 parts by weight ofacrylonitrile and 6 parts by weight of methyl acrylate were mixed with410 parts by weight of water of an aqueous catalyst solution which wasprepared by dissolving 6.5 parts by weight of sodium metabisulfite and0.8 parts by weight of sodium nitrite into 20 parts by Weight of waterand reacting them at a pH of 5.0 at a temperature of 55 C. for 10minutes. In this case, it was expected that the polymerization would becompleted in a concentration of noncopolymerized monomers in water of6.0% by weight.

The point having the co-ordinates (73, 6.0) is contained within thequadrilateral ABCD defined in the accompanying drawing. Thepolymerization mixture was adjusted to a pH of 2.5 by using sulfuricacid, and then polymerized at a temperature of 48 C. for hours in apolymerization reactor. A copolymer consisting of 94.1% by weight ofacrylonitrile and 5.9% by weight of methyl acrylate was isolated in ayield of 73% by weight.

The concentration of the non-copolymerized monomer in water was 6.0% byweight.

The resultant copolymer was subjected to the same filament manufacturingprocess as that of Example 1. The acrylonitrile copolymer filamentobtained had a superior whiteness of 98.8.

For comparison, an acrylonitrile-methyl acrylate copolymer filament wasprepared by the following process different from that of the presentinvention.

A mixture of 93 parts by weight of acrylonitrile and 7 parts by weightof methyl acrylate was dissolved in 1,400 parts by weight of water.

A polymerization reactor filled by nitrogen gas was charged with themixture and then charged with an aqueous solution containing 7.5 partsby weight of sodium metabisulfite in 50 parts by weight of water Thereaction mixture in the reactor was adjusted to a pH of 2.2 using 1N-sulfuric acid and mixed with an aqueous solution of 0.75 parts byweight of sodium nitrite in 50 parts by weight of water.

The polymerization system thus prepared was polymerized at a temperatureof 58 C. for 5 hours. The resultant copolymer was filtered, washed withwater and dried. 70 parts by weight of copolymer consisting of 92% byweight of acrylonitrile and 8% by weight of methyl acrylate wasobtained. This showed that the yield of the copolymer was 70% based onthe initial total weight of the monomers, and the concentration ofnoncopolymerized monomers in water was 2.0% by weight.

In the accompanying drawing, it is clear that the point havingco-ordinates (70, 2.0) lies outside the quadrilateral ABCD.

The copolymer was dissolved in dimethyl acetamide in a concentration of23% by weight in order to prepare a spinning solution. The spinningsolution was subjected to conventional wet-spinning and then heatrelaxed at a temperature of 135 C.

The resultant filament had a low whiteness of 93.4.

In consideration of the whitenesses of the filaments of the presentexample and the comparison example, it

was concluded that the acrylonitrile copolymer prepared by the processaccording to the present invention is capable of the formingacrylonitrile copolymer filaments having an excellent whiteness andheat-stability.

EXAMPLE 3 In order to prepare an acrylonitrile copolymer in a yield of81% based on the initial total weight of comonomers, 91 parts by weightof acrylonitrile and 9 parts by weight of vinyl acetate were mixed with260 parts by weight of water and an aqueous catalyst solution. In thiscase, it was expected that the polymerization would be completed in aconcentration of non-copolymerized comonomers which remained in water of5.94% by weight.The point having the co-ordinates (8 1, 5.94) is withinthe quadrilateral ABCD defined in the accompanying drawing. The catalystsolution was prepared by the procedure wherein an aqueous solution of7.5 parts by weight of sodium sulfite in 20 parts by weight of water ismixed with an aqueous solution of 0.6 part by weight of sodium nitritein 20 parts by weight of water the mixture solution adjusted to a pH of5.5 by using an aqueous solution of sodium bicarbonate in 20 parts byweight of water, and reacted at a temperature of 30 C. for 30 minuteswhile stirring.

The polymerization mixture was heated at a temperature of 42 C. for 4hours in order to copolymerize the comonomers. The resultant copolymerwas filtered and dried. The yield of the copolymer was 81% by weight andtherefore, the concentration of the non-copolymerized comonomers inwater was 5.94% by weight. The copolymer consisted of 93% by weight ofacrylonitrile and 7% by weight of vinyl acetate.

The copolymer was dissolved into dimethyl acetamide in a concentrationof 25% by weight, and from the resultant solution, an acrylonitrilecopolymer filament was prepared by the conventional wet-spinning method.

The resultant acrylonitrile copolymer filament had a superior whitenessof 99.2.

For comparison, an aqueous solution of 91 parts by weight ofacrylonitrile and 9 parts by weight of vinyl acetate in 250 parts byweight of water was charged into a polymerization reactor being filledwith nitrogen gas, an aqueous solution of 5 parts by weight of sodiumsulfite in 10 parts by weight of water was added to the comonomersolution, and then an aqueous solution of 0.8 part by weight of sodiumnitrite in 10 parts by weight of water was added to the mixture.

The reaction mixture was adjusted to a pH of 2.4 by adding 10 parts byweight of water containing sodium bicarbonate and then maintained at atemperature of 60 C. for 10 hours in order to copolymerize thecomonomers. The resultant copolymer was filtered and dried. Thecopolymer consisted of 93% by weight of acrylonitrile and 7% by weightof vinyl acetate. The yield was 90% based on the initial total weight ofthe comonomers, and therefore, the concentration of the non-polymerizedc0mOnomers in water was 3.6% by weight. It was observed that the pointhaving coordinate (90, 3.6) lies outside the quadrilateral ABCD definedin the accompanying drawing.

The copolymer filament which was prepared by the same procedure as thatof the present example, had a low whiteness of 93.1.

EXAMPLE 4 In order to prepare an acrylonitrile copolymer in a yield ofbased on the initial total weight of comonomers, 93% by weight ofacrylonitrile and 7% by weight of methyl methacrylate were mixed in 700parts by weight of water in the presence of 7.5 parts by weight ofsodium hydrogensulfite and 0.75 part by weight of sodium nitrite. Inthis case it Was expected that when the polymerization of the comonomerswas finished, the concentration of non-copolymerized comonomers in waterwould be 2.14% by weight. The point having co-ordinates (85, 2.14) is 7within the quadrilateral ABCD defined in the accompanying drawing. Thereaction mixture was adjusted to a pH of 2.5 by adding sulfuric acid,and then heated at a temperature'of 50 C. for 7 hours.

A copolymer was obtained in a yield of 85% by weight. The concentrationof non-polymerized comonomers in water was 2.14%.

The resultant copolymer was dissolved in dimethyl acetamide in aconcentration of 22% by weight and then the solution was wet-spun, drawnand heat-relaxed in the same procedure as that of Example 1. Theresultant filament had a high whiteness of 99.0.

EXAMPLE In order to prepare an acrylonitrile copolymer in a yield of92.5% based on the initial total weight of comonomers, 92 parts byweight of acrylonitrile 7 parts by weight of vinyl acetate and 1 part byweight of dimethyl acrylamide were mixed with 750 parts by weight ofwater, and then 0.8 part by weight of sodium nitrite and 5.0 parts byweight of sodium metabisulfite were added to the mixture.

In this case, it was expected that when the polymerization of thecomonomers was finished, the concentration of non-polymerized comonomersin water would be 1.0% by weight. The point having co-ordinates (92.5,1.0) is within the quadrilateral ABCD in the accompanying drawing.

The reaction mixture was polymerized at a temperature of 58 C. for 10hours. The yield of the copolymer was 92.5%, and the concentration ofthe non-polymerized comonomers in water was 1.0% by weight.

The resultant copolymer was dissolved in dimethyl acetamide in aconcentration of 24% by weight, and then the solution was wet-spun,drawn and heat-relaxed using the same procedure as that of Example 1.

The resultant filament had a superior whiteness of 96.7.

EXAMPLE 6 In order to prepare an acrylonitrile copolymer in a yield of96%, 94 parts by weight of acrylonitrile and 6 parts by weight of methylacrylate were mixed with 450 parts by weight of water.

An aqueous catalyst solution was prepared by dissolving 5 parts byweight of sodium hydrogensulfite and 0.8 parts by weight of sodiumnitrite in 50 parts by weight of Water, reacting them at a pH of 5.0which was adjusted by sulfuric acid, for 10 minutes, adjusting it to apH of 2.5 by adding sulfuric acid and then further reacting them at atemperature of 55 C. for 10 minutes. The catalyst solution thus preparedwas mixed with the comonomer mixture.

It was expected that when the polymerization of the comonomers wasfinished, the concentration of non-polymerized comonomer in water wouldbe 0.82% by weight. The point having co-ordinate (96, 0.82) lies withinthe quadrilateral ABCD of the accompanying drawing.

The reaction mixture was polymerized at a temperature of 52 C. for 11hours at a pH of 2.5 which was adjusted by sulfuric acid.

A copolymer having an excellent whiteness was obtained at a yield of 96%by weight. The concentration of the non-polymerized comonomers in waterwas 0.82%.

The resultant copolymer was dissolved in dimethyl formamide in aconcentration of 28.6% by weight, and the solution was wet-spun drawnand heat-relaxed using the same procedure as that of Example 1.

The resultant filament had an excellent whiteness of 98.6.

What we claim is:

1. In the method for the manufacture of a homopolymer or copolymer ofacrylonitrile having an excellent whiteness by polymerizing at atemperature of 4060 C. in an acidic aqueous medium having a pH of 2.0 to3.0, a monomeric material containing at least 50% by weight ofacrylonitrile in the presence of a redox catalyst containing nitrousacid or its salt and a reducing sulfoxyl compound yielding a polymer ofto 96% by weight based on the initial weight of monomer, the improvementwhich comprises,

adjusting the concentration of said monomeric material to a value whichsatisfies the condition that when the polymerization is completed insaid yield of the resultant polymer, the concentration ofnon-polymerized monomeric material in water is on or within aquadrilateral defined by the drawing, in a rectangular co-ordinatesystem having the ordinate representing the concentration in percentageof said non-polymerized monomeric material in water and the abscissarepresenting the yield in percentage of said resultant polymer, byco-ordinates A (70, 10), B (70, 3.33), C (96, 0.44) and D (96, 1.33).

References Cited UNITED STATES PATENTS 3,213,069 10/1965 Rausch 26085.5N

OTHER REFERENCES Schnecko, Chem. ABS., 59, p. 1024lf (1963). Chem. ABS.,62, p. 5411c (1965).

HARRY WONG, 111., Primary Examiner U.S. c1. xn. 260-325 N, 79.3 M, 85.5D, 85.5 P, 88.7 G

